High hydrostatic pressure effect on natural microflora, Saccharomyces cerevisiae, Escherichia coli, and Listeria Innocua in navel orange juice
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An isostatic pressure system was used to treat fresh-squeezed orange juice inoculated with Saccharomyces cerevisiae, Escherichia coli, and Listeria innocua for selected times (come-up time, CUT, to 15 min plus CUT) and pressures (103 - 414 MPa). Specific agars, for each type of microorganism, were used for pour plating to count survivors after pressure treatment. Decimal reduction time values (Dp) were calculated from the first order kinetics modeling for S. cerevisiae (103-241 MPa), E. coli (103-241 MPa), and L. innocua (103-345 MPa) survivors in juice. Dp values of 6.1-52.1, 0.6-14.9, and 4.8-357.1 min were obtained for S. cerevisiae, E. coli, and L. innocua, respectively. zp values of 147.1, 92.6, and 59.2 MPa were calculated for these microorganisms, respectively. The come-up time (CUT, time required to reach the processing pressure), had an important effect on the microbial reduction. The initial counts of 5.3 x 105, 1.2 x 107, and 2.6 x 107 CFU/mL were reduced by 30, 88, and 27 percent for S. cerevisiae, E. coli, and L. innocua, respectively, at 241 MPa, after 1.2, 3.0 and 1.8 min of processing, respectively. However, no survivors were observed (<10 CFU>/mL) for the three types of microorganisms when processing at 241 MPa for times longer than 3 min or pressures higher than 241 MPa. © 2011 Berkeley Electronic Press. All rights reserved.